Implant devices secured to bone or bone segments are utilized to promote the healing and repair of various parts of the human body. In some cases, the implant devices are secured to bone or bone segments such that the bones themselves heal, fuse, or stabilize relative to one another. In other cases, implant or fixation devices are used to secure bones or bone fragments such that the surrounding soft tissue may heal without being disturbed by relative movement of the bones.
During the surgical procedure to implant fixation devices, a plurality of bone screws or other fixation elements, in concert with coupling members, are secured to a plurality of respective bones. Each of the bone screws, or anchor members, is then secured relative to the others with an additional apparatus, such as a connecting member, brace or rod. A pedicle screw and rod system is one such example that is commonly used to secure adjacent vertebrae together in a desired relationship.
As an example, a patient may require that a number of vertebrae be secured so that fusion of the bones may take place. To accomplish fusion a number of bone anchors may be secured to a plurality of vertebrae via threaded engagement or by hooks that engage anatomy about the vertebrae. Each bone anchor or hook may be integrally attached to a coupling member which often include upstanding walls forming a u-shape resembling a yoke. The coupling members may be integral with the anchor member head or may be movably attached and articulate relative to the anchor members. Each coupling member in turn may be secured relative to the other coupling members by a connecting member or rod. A locking device or cap is driven into each of the coupling members ultimately locking the rod relative to each coupling member.
When positioning a bone anchor or hook, the orientation of the anatomical structures often results in a skewed relationship of the coupling members relative to each other. The connecting member, once placed in the coupling members, is utilized to reorient the vertebrae in a more desirable relationship. Undesirable relationships of vertebrae are often attributed to disc collapse, trauma, or disease such as scoliosis. In the case of collapse, distraction of the vertebrae may be desirable. If the anchor, coupling member and rod accompany an interbody device, contraction of the vertebrae to promote fusion may be desirable. However in the case of trauma or scoliosis, the connecting member may be pre-bent in a predetermined manner conforming to the ultimate desired position of the vertebrae. The deformation, or bend, of the spinal connecting member takes the shape of the desired spinal alignment and thus will likely not conform to the skewed relationship of the coupling members. The connecting member or rod may need to be reduced and or rotated to be captured in the coupling members.
The reduction and rotation of spinal rods is currently accomplished by devices relying on threaded mechanisms for linear advancement of the rods into the coupling members. While these devices may be effective, they are typically complicated, bulky, involve many revolutions to achieve reduction, offer little in the way of tactile feed back to the operator, require two hands for the reduction process, and are not easily adapted to minimally invasive surgery.
Minimally invasive surgeries require that only small incisions be made (typically ¾″) in the skin of the patient posterior to each vertebrae requiring a spinal implant assembly. Tissues that impede entry to the surgical site are then distracted, and a pedicle screw assembly, typically attached to an anchor extension or yoke manipulator, is introduced to the surgical site. All subsequent procedures take place in or adjacent to the yoke manipulator including, but not limited to, rod reduction, rod rotation, and deployment and securance of a locking device. Typical instruments that perform rod reduction are not adaptable from open surgery techniques to the limited area afforded in minimally invasive surgery. In addition the complexity of current instruments, their method of operation, and the need for additional tools to complete the surgery lead to lengthier surgical times.